1. Field of the Invention:
The present invention is directed toward the field of cooling systems and more particularly to a passive means of cooling an enclosure containing electronics by providing an enclosure having an integral heat pipe incorporated into the enclosure.
2. Art Background:
It is common to those skilled in the art to house electronics, such as telecommunications, cable television and traffic light control equipment, in enclosures to protect them from contaminants in the surrounding environments, and to shield them from electromagnetic radiation. It is also well known that these electronics generate significant heat during operation, and this heat must be dissipated to prevent damage or destruction to the electronics. The dissipation of heat will ensure that the electronics operate only within a limited temperature range.
In the past, cooling of electronics was achieved by flowing a cooling fluid over and/or around the heat source. Once heated by the heat source, the cooling fluid was vented from the enclosure to conduct file heat away from the enclosure. One method used for cooling was heat exchangers which separately transferred heat from the enclosed heat source to an outside cooling medium. However, this presented a problem because the enclosure or electronics did not remain isolated from the outside environment and were susceptible to contaminants. Furthermore, to operate effectively, these types of heat exchangers required the use of one or more fans to force air across their surfaces. Or, in systems requiring extreme heat dissipation, a traditional refrigeration cycle was required. The fan or refrigeration cycle methods both required an additional power source along with moving parts and motors for operation. Since in some cases power was not available or access to the moving parts was difficult because the electronics were located in a remote location, methods as described above were not generally practical.
Furthermore, many prior art devices have completely buried the electronics underground. Burying the electronics made access to the electronics very difficult for repair and maintenance purposes. Moreover, wholes dug in the ground to receive the enclosures were irregular in shape, thereby creating air pockets between the enclosure and the surrounding soil. These air pockets made it difficult to transfer any considerable amount of heat generated by electronic components to the surrounding soil. As a result of these problems, it has been discovered that more efficient cooling of electronics can be obtained through the use of passive heat pipes which require no external power source and contain no moving parts.
Generally, the heat pipe is in the form a vacuum-tight vessel in a particular geometric shape which is evacuated and partially filled with a working fluid. The heat pipe passively transfers heat from a heat source to a heat sink where heat is dissipated. As the heat is conducted into the heat pipe, the fluid is vaporized in an evaporator section creating a pressure gradient in the heat pipe. This forces the vapor to flow along the heat pipe to the condenser section, where the vaporized fluid is condensed and turned back to its fluid state by giving up its latent heat of vaporization. The working fluid is then returned to the evaporator section to repeat the process of removing the heat generated by the heat source.
One method used to achieve cooling by use of a heat pipe places the evaporator section at the lower end and the condenser section at the upper end where the heat pipe is in a substantially vertical position. Once the working fluid has been condensed, the liquid flows by gravity back to the evaporator section. Although no wicking structure is needed to return the working fluid to the evaporator section, this method is less efficient than the present invention wherein the evaporator section is located at the top of the enclosure because heat naturally migrates in an upward direction. Furthermore, when the condenser section is placed at the upper end, the system is less efficient because the temperature of the ground is lower than the temperature of the outside environment. Placing the condenser section at the lower end serves as a more effective way of dissipating heat.